Lithographic apparatus, device manufacturing method, and device manufactured thereby

ABSTRACT

A lithographic projection apparatus comprises a vacuum chamber having a wall enclosing at least one of first and second object tables, the or each object table within the vacuum chamber being connected to positioning means for positioning the object table with respect to a projection system of the apparatus. The positioning means is provided with a pneumatic gravity compensator comprising a piston associated with the object table; a gas-filled pressure chamber, the gas in the pressure chamber acting on the movable member to at least partially counteract the weight of the object table; a gas bearing; and evacuating means for evacuating gas escaping through a gap between the movable member and a bearing surface of a cylindrical housing towards the vacuum chamber. A partially flexible rod connects the piston to the object table.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to a lithographicprojection apparatus and more specifically to a lithographic projectionapparatus including a radiation system for supplying a projection beamof radiation, a support to support patterning structure, the patterningstructure serving to pattern the projection beam according to a desiredpattern, a substrate table to hold a substrate, and a projection systemto project the patterned beam onto a target portion of the substrate.

[0003] 2. Description of the Related Art

[0004] The terms “patterning means”, “patterning structure” or “mask” ashere employed should be broadly interpreted as referring to means thatcan be used to endow an incoming radiation beam with a patternedcross-section, corresponding to a pattern that is to be created in atarget portion of the substrate; the term “light valve” can also be usedin this context. Generally, the pattern will correspond to a particularfunctional layer in a device being created in the target portion, suchas an integrated circuit or other device (see below). Examples of suchpatterning means include:

[0005] A mask. The concept of a mask is well known in lithography, andit includes mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. Placementof such a mask in the radiation beam causes selective transmission (inthe case of a transmissive mask) or reflection (in the case of areflective mask) of the radiation impinging on the mask, according tothe pattern on the mask. In the case of a mask, the support structurewill generally be a mask table, which ensures that the mask can be heldat a desired position in the incoming radiation beam, and that it can bemoved relative to the beam if so desired.

[0006] A programmable mirror array. An example of such a device is amatrix-addressable surface having a viscoelastic control layer and areflective surface. The basic principle behind such an apparatus is that(for example) addressed areas of the reflective surface reflect incidentlight as diffracted light, whereas unaddressed areas reflect incidentlight as undiffracted light. Using an appropriate filter, theundiffracted light can be filtered out of the reflected beam, leavingonly the diffracted light behind; in this manner, the beam becomespatterned according to the addressing pattern of the matrix-addressablesurface. The required matrix addressing can be performed using suitableelectronic means. More information on such mirror arrays can be gleaned,for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, which areincorporated herein by reference. In the case of a programmable mirrorarray, the support structure may be embodied as a frame or table, forexample, which may be fixed or movable as required.

[0007] A programmable LCD array. An example of such a construction isgiven in U.S. Pat. No. 5,229,872, which is incorporated herein byreference. As above, the support structure in this case may be embodiedas a frame or table, for example, which may be fixed or movable asrequired.

[0008] For purposes of simplicity, the rest of this text may, at certainlocations, specifically direct itself to examples involving a mask andmask table; however, the general principles discussed in such instancesshould be seen in the broader context of the patterning means as hereinset forth above.

[0009] Lithographic projection apparatus can be used, for example, inthe manufacture of integrated circuits (ICs). In such a case, thepatterning structure may generate a circuit pattern corresponding to anindividual layer of the IC, and this pattern can be imaged onto a targetportion (e.g. comprising one or more dies) on a substrate (siliconwafer) that has been coated with a layer of radiation-sensitive material(resist). In general, a single wafer will contain a whole network ofadjacent target portions that are successively irradiated via theprojection system, one at a time. In current apparatus, employingpatterning by a mask on a mask table, a distinction can be made betweentwo different types of machine. In one type of lithographic projectionapparatus, each target portion is irradiated by exposing the entire maskpattern onto the target portion at once; such an apparatus is commonlyreferred to as a wafer stepper. In an alternative apparatus—commonlyreferred to as a step-and-scan apparatus—each target portion isirradiated by progressively scanning the mask pattern under theprojection beam in a given reference direction (the “scanning”direction) while synchronously scanning the substrate table parallel oranti-parallel to this direction; since, in general, the projectionsystem will have a magnification factor M (generally <1), the speed V atwhich the substrate table is scanned will be a factor M times that atwhich the mask table is scanned. More information with regard tolithographic devices as here described can be gleaned, for example, fromU.S. Pat. No. 6,046,792, incorporated herein by reference.

[0010] In a manufacturing process using a lithographic projectionapparatus, a pattern (e.g. in a mask) is imaged onto a substrate that isat least partially covered by a layer of radiation-sensitive material(resist). Prior to this imaging step, the substrate may undergo variousprocedures, such as priming, resist coating and a soft bake. Afterexposure, the substrate may be subjected to other procedures, such as apost-exposure bake (PEB), development, a hard bake andmeasurement/inspection of the imaged features. This array of proceduresis used as a basis to pattern an individual layer of a device, e.g. anIC. Such a patterned layer may then undergo various processes such asetching, ion-implantation (doping), metallization, oxidation,chemo-mechanical polishing, etc., all intended to finish off anindividual layer. If several layers are required, then the wholeprocedure, or a variant thereof, will have to be repeated for each newlayer. Eventually, an array of devices will be present on the substrate(wafer). These devices are then separated from one another by atechnique such as dicing or sawing, whence the individual devices can bemounted on a carrier, connected to pins, etc. Further informationregarding such processes can be obtained, for example, from the book“Microchip Fabrication: A Practical Guide to Semiconductor Processing”,Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN0-07-067250-4, incorporated herein by reference.

[0011] For the sake of simplicity, the projection system may hereinafterbe referred to as the “lens”; however, this term should be broadlyinterpreted as encompassing various types of projection system,including refractive optics, reflective optics, and catadioptricsystems, for example. The radiation system may also include componentsoperating according to any of these design types for directing, shapingor controlling the projection beam of radiation, and such components mayalso be referred to below, collectively or singularly, as a “lens”.Further, the lithographic apparatus may be of a type having two or moresubstrate tables (and/or two or more mask tables). In such “multiplestage” devices the additional tables may be used in parallel, orpreparatory steps may be carried out on one or more tables while one ormore other tables are being used for exposures. Twin stage lithographicapparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO98/40791, incorporated herein by reference.

[0012] In a lithographic apparatus, the size of features that can beimaged onto the wafer is limited by the wavelength of the projectionradiation. To produce integrated circuits with a higher density ofdevices and hence higher operating speeds, it is desirable to be able toimage smaller features. While most current lithographic projectionapparatus employ ultraviolet light generated by mercury lamps or excimerlasers, it has been proposed to use shorter wavelength radiation ofaround 13 nm. Such radiation is termed extreme ultraviolet (EUV) or softx-ray, and possible sources include laser-produced plasma sources,discharge sources or synchrotron radiation from electron storage rings.An outline design of a lithographic projection apparatus usingsynchrotron radiation is described in “Synchrotron radiation sources andcondensers for projection x-ray lithography”, J B Murphy et al, AppliedOptics Vol. 32 No. 24 pp 6920-6929 (1993).

[0013] Other proposed radiation types include electron beams and ionbeams. These types of beam share with EUV the requirement that the beampath, including the mask, substrate and optical components, be kept in ahigh vacuum. This is to prevent absorption and/or scattering of thebeam, whereby a total pressure of less than about 10⁻⁶ millibar istypically necessary for such charged particle beams. Wafers can becontaminated, and optical elements for EUV radiation can be spoiled, bythe deposition of carbon layers on their surface, which imposes theadditional requirement that hydrocarbon partial pressures shouldgenerally be kept below 10⁻⁸ or 10⁻⁹ millibar. Otherwise, for apparatususing EUV radiation, the total vacuum pressure need only be 10⁻³ or 10⁻⁴mbar, which would typically be considered a rough vacuum. Furtherinformation with regard to the use of electron beams in lithography canbe gleaned, for example, from U.S. Pat. No. 5,079,122 and U.S. Pat. No.5,260,151, as well as from EP-A-0 965 888, which are incorporated byreference.

[0014] Working in such a high vacuum imposes quite onerous conditions onthe components that must be put into the vacuum and on the vacuumchamber seals, especially those around any part of the apparatus where amotion must be fed-through to components inside the chamber from theexterior. For components inside the chamber, materials that minimise oreliminate contaminant and total outgassing, i.e. both outgassing fromthe materials themselves and from gases adsorbed on their surfaces,should be used.

[0015] For certain applications, a gravity compensator is required toexert a bias force that at least partially counteracts the weight of anobject to be supported and which compensator largely preventstransmission of vibrations in the support direction. The height of theobject may be varied by motors, and the application of a gravitycompensator relieves the motors of supplying a force to overcomegravity, leading to a considerable reduction in power consumption andheating of the motors. However, such gravity compensators having apneumatic working principle are known, but their application in a vacuumenvironment is presently not feasible, since the possible escape of gasfrom the gravity compensator would seriously disturb the vacuum. Toprevent transmission of vibrations in a horizontal direction, it isknown to provide a supporting means, such as a pneumatic gravitycompensator, with a horizontal air bearing. Gas flowing out of thehorizontal gas bearing will seriously disturb the vacuum. Abovesupporting means are described in EP 0 973 067, which is incorporatedherein by reference.

SUMMARY OF THE INVENTION

[0016] A lithographic projection apparatus in accordance with one aspectof the present invention includes a radiation system for providing aprojection beam of radiation, a support structure to support patterningstructure, the patterning structure serving to pattern the projectionbeam according to a desired pattern, a substrate table to hold asubstrate, a projection system to project the patterned beam onto atarget portion of the substrate, and a supporting structure comprising asupport member having a finite stiffness in a perpendicular directionthat is substantially perpendicular to a support direction of thesupport member.

[0017] In a further embodiment of the present invention, the apparatusfurther comprises a vacuum chamber having a wall enclosing the supportmeans, wherein the supporting means further comprises a gas-filledpressure chamber, the gas in the pressure chamber acting on a movablemember such as to at least partially counteract a force substantiallyparallel to the support direction, and evacuating means constructed andarranged so as to evacuate gas escaping towards the vacuum chamberthrough a gap between the movable member and a bearing surface.

[0018] According to yet a further aspect of the invention there isprovided a method of manufacturing a device including providing asubstrate that is at least partially covered by a layer of radiationsensitive material, providing a projection beam of radiation using aradiation system, using patterning structure to endow the projectionbeam with a pattern in its cross-section, projecting the patterned beamof radiation onto a target portion of the layer of radiation-sensitivematerial; and

[0019] providing an isolated reference frame characterized by supportingone of the support structure, the substrate table and the isolatedreference frame with a support member having a finite stiffness in aperpendicular direction that is substantially perpendicular to a supportdirection of the support member.

[0020] Although specific reference may be made in this text to the useof the apparatus according to the invention in the manufacture of ICs,it should be explicitly understood that such an apparatus has many otherpossible applications. For example, it may be employed in themanufacture of integrated optical systems, guidance and detectionpatterns for magnetic domain memories, liquid-crystal display panels,thin-film magnetic heads, etc. The skilled artisan will appreciate that,in the context of such alternative applications, any use of the terms“reticle”, “wafer” or “die” in this text should be considered as beingreplaced by the more general terms “mask”, “substrate” and “targetportion”, respectively.

[0021] In the present document, the terms “radiation” and “beam” areused to encompass all types of electromagnetic radiation, includingultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or126 nm) and EUV (extreme ultra-violet radiation, e.g. having awavelength in the range 5-20 nm), as well as particle beams, such as ionbeams or electron beams.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention and its attendant advantages will be furtherelucidated with the aid of an exemplary Embodiment and the accompanyingschematic drawings, in which:

[0023]FIG. 1 depicts a lithographic projection apparatus according to anembodiment of the invention;

[0024]FIG. 2 depicts part of short-stroke positioning means according tothe invention;

[0025]FIG. 3 depicts a detail of evacuating means according to theinvention;

[0026]FIG. 4a depicts a schematic representation of a mass on a hingedlyconnected rigid rod; and

[0027]FIG. 4b depicts a schematic representation of a mass on a rigidlyconnected flexible rod.

[0028]FIG. 5 depicts part of short-stroke positioning means according toembodiment 2 of the present invention.

[0029]FIG. 6 depicts a schematic representation of a supporting meansaccording to embodiment 3.

[0030] Corresponding features in the various figures are denoted by thesame reference symbols.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Embodiment 1

[0032]FIG. 1 schematically depicts a lithographic projection apparatusaccording to a particular embodiment of the invention. The apparatuscomprises:

[0033] a radiation system Ex, IL, for supplying a projection beam PB ofradiation (e.g. UV or EUV radiation, electrons or ions). In thisparticular case, the radiation system also comprises a radiation sourceLA;

[0034] a first object table (mask table) MT provided with a mask holderfor holding a mask MA (e.g. a reticle), and connected to firstpositioning means for accurately positioning the mask with respect toitem PL;

[0035] a second object table (substrate table) WT provided with asubstrate holder for holding a substrate W (e.g. a resist-coated siliconwafer), and connected to second positioning means for accuratelypositioning the substrate with respect to item PL;

[0036] a projection system (“lens”) PL (e.g. a refractive orcatadioptric system, a mirror group or an array of field deflectors) forimaging an irradiated portion of the mask MA onto a target portion C(e.g. comprising one or more dies) of the substrate W.

[0037] As here depicted, the apparatus is of a reflective type (i.e. hasa reflective mask). However, in general, it may also be of a refractivetype, for example (with a transmissive mask). Alternatively, theapparatus may employ another kind of patterning means, such as aprogrammable mirror array of a type as referred to above.

[0038] The source LA (e.g. an excimer laser, an undulator or wigglerprovided around the path of an electron beam in a storage ring orsynchrotron, a laser-produced plasma source, a discharge source or anelectron or ion beam source) produces a beam of radiation. This beam isfed into an illumination system (illuminator) IL, either directly orafter having traversed conditioning means, such as a beam expander, forexample. The illuminator may comprise adjusting means for setting theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in the beam. Inaddition, it will generally comprise various other components, such asan integrator and a condenser. In this way, the beam PB impinging on themask MA has a desired uniformity and intensity distribution in itscross-section.

[0039] It should be noted with regard to FIG. 1 that the source LA maybe within the housing of the lithographic projection apparatus (as isoften the case when the source LA is a mercury lamp, for example), butthat it may also be remote from the lithographic projection apparatus,the radiation beam which it produces being led into the apparatus (e.g.with the aid of suitable directing mirrors); this latter scenario isoften the case when the source LA is an excimer laser. The currentinvention and claims encompass both of these scenarios.

[0040] The beam PB subsequently intercepts the mask MA, which is held ona mask table MT. Having been reflected by the mask MA, the beam PBpasses through the lens PL, which focuses the beam PB onto a targetportion C of the substrate W. With the aid of the second positioningmeans (and interferometric measuring means IF), the substrate table WTcan be moved accurately, e.g. so as to position different targetportions C in the path of the beam PB. Similarly, the first positioningmeans can be used to accurately position the mask MA with respect to thepath of the beam PB, e.g. after mechanical retrieval of the mask MA froma mask library, or during a scan. In general, movement of the objecttables MT, WT will be realized with the aid of a long-stroke module(course positioning) and a short-stroke module (fine positioning), whichare not explicitly depicted in FIG. 1. However, in the case of a waferstepper (as opposed to a step-and-scan apparatus) the mask table MT mayjust be connected to a short-stroke actuator, or may be fixed.

[0041] The depicted apparatus can be used in two different modes:

[0042] 1. In step mode, the mask table MT is kept essentiallystationary, and an entire mask image is projected at once (i.e. a single“flash”) onto a target portion C. The substrate table WT is then shiftedin the x and/or y directions so that a different target portion C can beirradiated by the beam PB;

[0043] 2. In scan mode, essentially the same scenario applies, exceptthat a given target portion C is not exposed in a single “flash”.Instead, the mask table MT is movable in a given direction (theso-called “scan direction”, e.g. the y direction) with a speed v, sothat the projection beam PB is caused to scan over a mask image;concurrently, the substrate table WT is simultaneously moved in the sameor opposite direction at a speed V=Mv, in which M is the magnificationof the lens PL (typically, M=¼ or ⅕). In this manner, a relatively largetarget portion C can be exposed, without having to compromise onresolution.

[0044] The embodiment shown employs a projection beam of EUV radiationand is therefore provided with a vacuum environment, or chamber, 10since most gases tend to absorb the EUV radiation.

[0045]FIG. 2 shows a part of the short-stroke positioning meansconnected to the substrate table WT, which positioning means is employedfor fine positioning of the substrate W (not shown in FIG. 2) withrespect to the projection system PL. The lower part, or foot, 22 of theshown configuration is connected to the long-stroke positioning means(not shown) for coarse positioning of the substrate table WT withrespect to the projection system PL. This foot 22 is able to move overbase plate BP (shown in FIG. 1). The configuration as shown in FIG. 2 ismounted in vacuum chamber 10.

[0046] Substrate table WT may be changed in height with respect to lowerpart 22 with the aid of short-stroke motors taking the form of so-calledLorentz-force motors. One Lorentz-force motor 30 for changing the heightis schematically depicted in FIG. 2 and comprises a system of permanentmagnets 31 mounted such as to have an identical magnetic orientation anda system of electric conductors 32 that may carry an electrical currentfor generating a Lorentz force in the vertical Z-direction to vary thedistance in between substrate table WT and lower part 22. In general,more than one Lorentz-force motor for the vertical direction isprovided. The system of magnets 31 is secured to substrate table WT andthe system of electrical conductors 32 is secured to lower part 22.Further Lorentz-force motors (not shown) are present to horizontallydisplace, tilt and rotate substrate table WT with respect to lower part22. Dimensions of the Lorentz-force motors are chosen such that adisplacement induced by one Lorentz-force motor is not obstructed by theother Lorentz-force motors over a selected short-stroke range ofdisplacement.

[0047] A supporting means, or gravity compensator, 40 is provided to atleast substantially support substrate table WT against gravity withrespect to lower part 22. Lorentz-force motor 30 is therefore relievedof generating such a supporting force, which would lead to a high energydissipation in conductors 32. In general, more than one gravitycompensator will be provided.

[0048] Gravity compensator 40 comprises a cylindrical housing 41provided with a pressure chamber 42, and a piston 43 which is journaledrelative to said housing in the vertical, or support, direction. Housing41 is secured to lower part 22 and piston 43 is through a rod 50connected to substrate table WT. Pressure chamber 42 is in fluidcommunication with gas supply means G (not shown) via a channel 44 toprovide a gas having a predetermined pressure in the pressure chamber.In this manner a pneumatic supporting force is generated to verticallysupport piston 43 in housing 41 by the gas pressure present in pressurechamber 42 and acting on bottom surface 43 a of piston 43. The gassupply means regulates the pressure in pressure chamber 42 such that thepneumatic supporting force will support substrate table WT againstgravity. The supporting force is essentially constant, irrespective ofthe position of piston 43 in the vertical Z-direction.

[0049] For further details on long-stroke and short-stroke positioningmeans and on gravity compensators, one is referred to European patentapplication EP 0 973 067, which is incorporated herein by reference.

[0050] Gas may escape from pressure chamber 42 via the gap 45 in betweenpiston 43 and the inner wall of cylindrical housing 41 and enter vacuumchamber 10, which would substantially disturb the vacuum within thevacuum chamber. The inner wall of housing 41 acts as a bearing surfacefor piston 43. To prevent gas from escaping to vacuum chamber 1 0,gravity compensator 40 is provided with evacuating grooves 60 a, 60 b inits inner wall surrounding piston 43. Grooves 60 a, 60 b are viaconduits 61 a, 61 b connected to a vacuum pump P (not shown) and areservoir R (not shown), respectively, to draw gas from the grooves andgap 45. Gas escaping through gap 45 in between housing 41 and piston 43will thus substantially escape via grooves 60 a, 60 b to reservoir R andvacuum pump P, and not towards vacuum chamber 10. Vacuum groove 60 awill be set to a lower pressure than grooves 60 b. Depending on therequired vacuum level of chamber 10, more vacuum grooves may beprovided, each groove in a direction towards the vacuum chamber beingevacuated to a lower pressure level, i.e. a higher vacuum level.

[0051] As shown in FIG. 2, two gas bearings 70 are provided in betweenthe inner wall of housing 41 and piston 43. The gas bearings provide fora friction-less displacement of piston 43 within housing 41, so as toprevent a transmission of vibrations from lower part 22 to substratetable WT in the vertical direction. Gas at a pressure of a few bars isintroduced from a gas supply G via conduits 71 to gap 45 to establishthe gas bearings 70. Grooves 60 b are provided aside the gas bearings toevacuate gas introduced from gap 45, so as to prevent the escape of gasto vacuum chamber 10 and to provide for stable gas bearings 70. In theembodiment shown, the gas bearings are set to an identical pressure.

[0052] However, the pressure may be set to different pressures byseparated conduits 71 in a further embodiment. Further, more than two orjust one gas bearing may be provided.

[0053]FIG. 3 shows a detail of air bearing 70 and pressure reliefstructure including evacuating grooves 60 a, 60 b. Air bearing 70 may beset to a pressure of 6 bar and grooves 60 b allow gas to escape to areservoir R at atmospheric pressure. Vacuum groove 60 a is connected toa vacuum pump P (not shown) that allows evacuating to a pressure levelof 1.5 mbar. Gaps having a length of 5-10 mm and a width of 2-25 μm inbetween gas bearing 70 and groove 60 b, groove 60 b and groove 60 a, andgroove 60 a and vacuum chamber allow a vacuum of 5×10⁻⁷ mbar to bereached within vacuum chamber 10. FIG. 3 also shows a further vacuumgroove 60 c connected to a further vacuum pump P2 to allow an evenhigher vacuum to be reached in vacuum chamber 10.

[0054] Rod 50 connects piston 43 to substrate table WT and allows fordisplacement of upper part in a horizontal XY-plane, i.e. perpendicularto the support direction. The configuration of rod 50 is chosen suchthat it stably supports substrate table WT, but also allows displacementin the horizontal plane with negligible or no force exerted on thesubstrate table in the horizontal direction. A transmission ofvibrations to the substrate table in the horizontal plane is thereforelargely prevented. FIGS. 4a and 4 b further demonstrate aboverequirements for rod 50.

[0055] A mass M1 supported by a rigid rod Rd1 that is hingedly connectedto mass M1 and supporting surface S1 will, due to gravity acting alongthe vertical support direction, exert a force F1 in the horizontal planeon some support S2 when mass M1 is not exactly positioned above theconnection of rod Rd1 to supporting surface S1, i.e. when M1 isdisplaced with respect to the vertical V, its gravitational equilibriumstate. Such a situation is shown in FIG. 4a. A flexible rod Rd2 that isrigidly secured to both mass M2 and supporting surface S1 will exert aforce F2 in the horizontal plane on mass M2 when the latter is displacedfrom the vertical V and the bottom surface of mass M2 is kept parallelto supporting surface S1, as is shown in FIG. 4b, such that a bendingmoment is exerted on flexible rod Rd2. However, mass M2 will also exerta force F1 on rod Rd2 as is explained with reference to FIG. 4a, forceF1 being opposed to force F2. The configuration of rod Rd2 may be chosensuch that forces F1 and F2 will at least substantially cancel eachother. Mass M2 will then stably balance on rod Rd2 and may be displacedin the horizontal XY-plane around vertical V without a substantial forcebeing exerted on mass M2. The gravity force acting parallel to thesupport direction thus provides a so called “negative stiffness” to rod50.

[0056] Rod 50 in FIG. 2 is configured, i.e. has stiffness in a directionperpendicular to the support direction, such that the situation asexplained with reference to FIG. 4b is applicable. The rod may be madeof a solid material having a uniform stiffness throughout its length,but the rod may also comprise (as shown in FIG. 2) a rigid intermediatepart 51 and two flexible parts 52. One flexible part is rigidly securedto piston 43 and the other flexible part is rigidly secured to substratetable WT. The elasticity, length and cross-sectional shape of theflexible parts have to be chosen so as to comply with a selected lengthof rod 50 and the mass of substrate table WT, such that the situation asexplained with regard to FIG. 4b holds.

[0057] Embodiment 2

[0058]FIG. 5 shows schematically a supporting means 40 according to asecond embodiment in which rod 50 is provided with a hollow part.Through the hollow part a conduit may be fed, through which, forexample, a liquid (e.g. cooling water) or an electrical or signalconnection is provided to the substrate table WT. Conduits are generallymade of materials that tend to release undesirable contaminants in avacuum environment. The proposed arrangement prevents suchcontamination.

[0059] Embodiment 3

[0060]FIG. 6 depicts schematically a means 40 according to a thirdembodiment of the invention. In the third embodiment a supported masktable MT is provided below a supporting upper part 22 that is connectedto long-stroke positioning means. The various parts as described for thefirst embodiment can also be distinguished in FIG. 6. The figure furthershows that conduits 61 are provided separate from rod 50. A bellows 60is provided through which conduits 60 is passed to mask table MT. Bothbellows 60 and conduits 60 provide an additional stiffness in thehorizontal direction, that is, they act as auxiliary support structures.To compensate for such an extra stiffness and, moreover, to generallyprovide for an adjustable negative stiffness, there is provided a meansto generate an adjustable force AF along the support direction. Force AFmay be accomplished by addition of an (extra) mass on the mask table MT,by using an (adjustable) spring or by applying air pressure, forexample.

[0061] While specific embodiments of the invention are disclosed above,it will be appreciated that the invention may be practiced other thandescribed. The description is not intended to limit the invention. Forinstance, the invention has been described with reference to a wafer orsubstrate table, but is also applicable to a mask table or vice versa.

1. A lithographic projection apparatus comprising: a radiation systemwhich provides a projection beam of radiation; a patterning structuresupport to support projection beam patterning structure which patternsthe projection beam according to a desired pattern; a substrate table tohold a substrate; a projection system which projects the patterned beamonto a target portion of the substrate; and a support member, supportinga portion of the lithographic projection apparatus and having a finitestiffness in a direction that is substantially perpendicular to asupport direction of the support member.
 2. An apparatus according toclaim 1, wherein the stiffness of the support member is such that adeformation force in the perpendicular direction by the support memberdue to a deformation of the support member in the perpendiculardirection substantially counteracts an opposite displacing force in theperpendicular direction due to a force substantially parallel to thesupport direction acting on the support member.
 3. An apparatusaccording to claim 1, wherein the support member comprises a rod.
 4. Anapparatus according to claim 3, wherein the rod comprises a rigid partand a flexible part.
 5. An apparatus according to claim 1, wherein thesupport member is provided with a hollow part.
 6. An apparatus accordingto claim 5, wherein a conduit is arranged through the hollow part.
 7. Anapparatus according to claim 1, wherein an auxiliary support structureto apply an additional force on the support member along the supportdirection is provided.
 8. An apparatus according to claim 1, furthercomprising a vacuum chamber having a wall enclosing the support member,wherein the support member further comprises: a gas-filled pressurechamber, the gas in the pressure chamber acting on a movable member suchas to at least partially counteract a force substantially parallel tothe support direction, and pressure relief structure allowing evacuationof gas escaping towards the vacuum chamber through a gap between themovable member and a bearing surface.
 9. An apparatus according to claim8, wherein the support member is connected to the movable member.
 10. Anapparatus according to claim 8, wherein the supporting member furthercomprises a bearing supporting the movable member and maintaining thegap between the movable member and the bearing surface, the bearingcomprising a gas bearing for providing pressurized gas into the gapthereby generating forces tending to hold the movable member away fromthe bearing surface, and the evacuating means being provided between thegas bearing and the vacuum chamber along the movable member so as toremove gas from the gap.
 11. An apparatus according to claim 10, whereinthe gas bearing comprises an elongate groove in one surface defining thegap; and a gas supply which supplies gas under pressure to said elongategroove.
 12. An apparatus according to claim 8, wherein the pressurerelief structure comprises a conduit providing a fluid communicationbetween the gap and at least one reservoir at a pressure higher thanthat of the vacuum chamber and lower than that of the gas to be removedfrom the gap.
 13. An apparatus according to claim 12, wherein theconduit comprises at least one elongate groove in a surface defining thegap.
 14. An apparatus according to claim 8, wherein the pressure reliefstructure includes a fluid communication between the gap and at leastone vacuum pump.
 15. An apparatus according to claim 14, wherein thefluid communication between the gap and the at least one vacuum pumpcomprises at least one elongate vacuum groove in a surface defining thegap.
 16. An apparatus according to claim 15, wherein the fluidcommunication comprises more than one elongate vacuum groove in thesurface defining the gap, the vacuum grooves being generally paralleland each of the respective grooves being in communication with aprogressively deeper vacuum in the direction of the vacuum chamber. 17.An apparatus according to claim 8, wherein the movable member comprisesa piston being journaled in a housing provided with the gas-filledpressure chamber, an inner wall of the housing providing the bearingsurface.
 18. An apparatus according to claim 1, wherein the supportmember supports one of the patterning structure support and thesubstrate table
 19. An apparatus according to claim 1, wherein thesupport structure comprises a mask table for holding a mask.
 20. Anapparatus according to claim 1, wherein the apparatus further comprisesan isolated reference frame, and the support member is arranged tosupport the isolated reference frame.
 21. An apparatus according toclaim 1, wherein the radiation system comprises a radiation source. 22.A device manufacturing method using a lithographic projection apparatuscomprising: providing a substrate that is at least partially covered bya layer of radiation-sensitive material; providing a projection beam ofradiation; patterning the projection beam of radiation with a pattern inits cross-section; projecting the patterned beam of radiation onto atarget portion of the layer of radiation-sensitive material, andsupporting one of a support structure of the lithographic projectionapparatus, a substrate table of the lithographic projection apparatusand an isolated reference frame of the lithographic projection apparatuswith a support member having a finite stiffness in a direction that issubstantially perpendicular to a support direction of the supportmember.
 23. A device manufactured according to the method of claim 22.